(a) Field of the Invention
The present invention concerns static induction thyristor having a high blocking voltage, a low forward voltage drop, and a high switching speed.
(b) Description of the Prior Art
Conventional thyristors, basically, are formed by a four-layer structure of pnpn. In such conventional thyristors it is difficult to carry out switching-off action using only a control or gate voltage. Further, even when cut-off is effected by this gate voltage, its speed is very low. In contrast thereto, static induction thyristor (hereinafter to be called SI-thyristor) is basically constructed by a gated diode structure, i.e. anode region, cathode region and gate means integrated in either of the anode or cathode region. The SI-thyristor has the features that turn off operation using the gate voltage is easy, and that its turn-off time is quick. However, the blocking voltage of the conventional SI thyristor is mainly determined by the thickness of a high-resistivity active region which, in turn, forms a limiting factor for the forward voltage drop. Therefore, simultaneous attainment of a high blocking voltage and a low forward voltage drop is difficult.